AMD-ify jQuery source

AMD is coming to jQuery. We'll divide up the source code into logical modules (starting with the modules that we currently have). The CDN build of jQuery will not include the AMD wrappers (the build process will get an update).

Some modules contain small blocks that cause the whole module to need a dependency. These small blocks have been separated into their own modules so they can be associated with their dependencies and optionally excluded. For instance, manipulation only requires ajax for evaluating scripts (see src/ajax/_evalUrl).